1. Field of the Invention
The present invention relates to a control method for an industrial vehicle, and to an industrial vehicle.
This application is based on Japanese Patent Application No. 2008-051053, the content of which is incorporated herein by reference.
2. Description of Related Art
Generally, in a hybrid system that combines an engine and a motor, a battery is widely used as a power source (refer, for example, to Japanese Unexamined Patent Application, Publication No. 2000-313600).
Among such batteries, the battery charge rate (below, the battery charge is referred to as the “battery SOC” (State of Charge)) must be controlled in those that are used in an HEV (Hybrid Electric Vehicle), and a variety of methods for controlling the battery SOC in hybrid systems have been proposed (refer, for example, to Japanese Unexamined Patent Application, Publication No. 2005-012902).
Specifically, in the case in which the battery SOC is high, the instantaneous charge capacity of the battery, that is, the amount of electric power by which the battery can be charged instantaneously, decreases. Thus, the battery SOC must be controlled so as to be equal to or less than a first prescribed value so that electric power that is generated during rotational regeneration can always be absorbed.
In contrast, the battery SOC must be controlled so as to be equal to or greater than a second prescribed value so that the battery SOC does not decrease excessively.
Thus, a variety of methods have been proposed for determining the battery SOC, and methods in which the battery SOC is determined by using the relationship between the battery voltage and the battery SOC are known.
In the case in which the battery SOC is determined by using these methods, there is a problem in that the battery voltage fluctuates significantly while charging and while discharging, and thus determining an accurate SOC is not possible.
Furthermore, although the battery SOC can be determined by using the relationship between the battery voltage and the battery SOC, a battery voltage that fluctuates significantly takes time to return to the original voltage, as described above, and thus, there is a problem in that determining the correct battery SOC takes time.
In contrast, the battery SOC must be controlled so as to maintain predefined values while supplying to a vehicle the power that is necessary for travel operations and load-handling operations, and thus, there is a problem in that power control becomes necessary. This power control determines, depending on the operational state of the vehicle, whether or not the battery can be charged and determines the amount of the charge.